https://github.com/offsetof created
https://github.com/llvm/llvm-project/pull/89449
This patch disables the relevant diagnostic in C++17 and later modes.
Fixes #45653
>From 44e3c7a4ced2ef1f8b78ab8b0009314fbcd05c6f Mon Sep 17 00:00:00 2001
From: offsetof <131769984+offse...@users.noreply.github.com>
Date: Fri, 19 Apr 2024 19:57:31 +0000
Subject: [PATCH] [clang] Allow constexpr relational comparison of unequal
"void*" values
Since C++17, it is no longer the case that applying relational operators
to unequal pointers to "void" always produces an unspecified result.
---
clang/lib/AST/ExprConstant.cpp | 5 ++++-
clang/test/AST/Interp/literals.cpp | 10 +++++-----
clang/test/CXX/drs/dr25xx.cpp | 1 +
clang/test/CXX/drs/dr26xx.cpp | 2 ++
clang/test/CXX/drs/dr27xx.cpp | 22 ++++++++++++++++++++++
clang/test/CXX/expr/expr.const/p2-0x.cpp | 23 +++++++++++++----------
clang/www/cxx_dr_status.html | 6 +++---
7 files changed, 50 insertions(+), 19 deletions(-)
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 73ae8d8efb23a2..2d480edab833c8 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -13510,7 +13510,10 @@ EvaluateComparisonBinaryOperator(EvalInfo &Info, const
BinaryOperator *E,
// operator is <= or >= and false otherwise; otherwise the result is
// unspecified.
// We interpret this as applying to pointers to *cv* void.
- if (LHSTy->isVoidPointerType() && LHSOffset != RHSOffset && IsRelational)
+ // This only applies until C++14; in C++17 a "cv void*" value can "point to
+ // an object" and is not treated specially in [expr.rel].
+ if (!Info.getLangOpts().CPlusPlus17 &&
+ LHSTy->isVoidPointerType() && LHSOffset != RHSOffset && IsRelational)
Info.CCEDiag(E, diag::note_constexpr_void_comparison);
// C++11 [expr.rel]p2:
diff --git a/clang/test/AST/Interp/literals.cpp
b/clang/test/AST/Interp/literals.cpp
index 277438d2e63114..91857228fcddc7 100644
--- a/clang/test/AST/Interp/literals.cpp
+++ b/clang/test/AST/Interp/literals.cpp
@@ -1,6 +1,6 @@
// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -Wno-vla
-fms-extensions -std=c++11 -verify=expected,both %s
// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -Wno-vla
-fms-extensions -std=c++20 -verify=expected,both %s
-// RUN: %clang_cc1 -std=c++11 -fms-extensions -Wno-vla -verify=ref,both %s
+// RUN: %clang_cc1 -std=c++11 -fms-extensions -Wno-vla
-verify=ref,ref-cxx11,both %s
// RUN: %clang_cc1 -std=c++20 -fms-extensions -Wno-vla -verify=ref,both %s
#define INT_MIN (~__INT_MAX__)
@@ -193,10 +193,10 @@ namespace PointerComparison {
/// FIXME: These two are rejected by the current interpreter, but
/// accepted by GCC.
- constexpr bool v5 = qv >= pv; // ref-error {{constant expression}} \
- // ref-note {{unequal pointers to void}}
- constexpr bool v8 = qv > (void*)&s.a; // ref-error {{constant expression}} \
- // ref-note {{unequal pointers to
void}}
+ constexpr bool v5 = qv >= pv; // ref-cxx11-error {{constant expression}} \
+ // ref-cxx11-note {{unequal pointers to void}}
+ constexpr bool v8 = qv > (void*)&s.a; // ref-cxx11-error {{constant
expression}} \
+ // ref-cxx11-note {{unequal pointers
to void}}
constexpr bool v6 = qv > null; // both-error {{must be initialized by a
constant expression}} \
// both-note {{comparison between '&s.b' and
'nullptr' has unspecified value}}
diff --git a/clang/test/CXX/drs/dr25xx.cpp b/clang/test/CXX/drs/dr25xx.cpp
index 62b2a0a088cc13..672979c2be8ef8 100644
--- a/clang/test/CXX/drs/dr25xx.cpp
+++ b/clang/test/CXX/drs/dr25xx.cpp
@@ -83,6 +83,7 @@ using ::cwg2521::operator""_div;
#endif
} // namespace cwg2521
+// cwg2526: sup 2749
#if __cplusplus >= 202302L
namespace cwg2553 { // cwg2553: 18 review 2023-07-14
diff --git a/clang/test/CXX/drs/dr26xx.cpp b/clang/test/CXX/drs/dr26xx.cpp
index f7a05b9827a235..de18787bcab96b 100644
--- a/clang/test/CXX/drs/dr26xx.cpp
+++ b/clang/test/CXX/drs/dr26xx.cpp
@@ -238,3 +238,5 @@ void test() {
}
}
#endif
+
+// cwg2696: dup 2749
diff --git a/clang/test/CXX/drs/dr27xx.cpp b/clang/test/CXX/drs/dr27xx.cpp
index 0434427d6c92a3..1f5b9e571079c9 100644
--- a/clang/test/CXX/drs/dr27xx.cpp
+++ b/clang/test/CXX/drs/dr27xx.cpp
@@ -10,6 +10,28 @@
// expected-no-diagnostics
#endif
+namespace cwg2749 { // cwg2749: 19
+#if __cplusplus >= 201703L
+
+constexpr bool f() {
+ int arr[2] {};
+ return (void*)arr < arr + 1;
+}
+static_assert(f());
+
+constexpr bool g() {
+ struct {
+ char c;
+ short s;
+ int i;
+ } s {};
+ return (void*)&s.c < &s.i;
+}
+static_assert(g());
+
+#endif
+}
+
namespace cwg2759 { // cwg2759: 19
#if __cplusplus >= 201103L
diff --git a/clang/test/CXX/expr/expr.const/p2-0x.cpp
b/clang/test/CXX/expr/expr.const/p2-0x.cpp
index e3cd057baba75f..54e163f05e4524 100644
--- a/clang/test/CXX/expr/expr.const/p2-0x.cpp
+++ b/clang/test/CXX/expr/expr.const/p2-0x.cpp
@@ -571,18 +571,21 @@ namespace UnspecifiedRelations {
// [expr.rel]p3: Pointers to void can be compared [...] if both pointers
// represent the same address or are both the null pointer [...]; otherwise
// the result is unspecified.
- struct S { int a, b; } s;
+ struct S { int a, b; static int c; } s;
constexpr void *null = 0;
- constexpr void *pv = (void*)&s.a;
- constexpr void *qv = (void*)&s.b;
+ constexpr void *av = (void*)&s.a;
+ constexpr void *bv = (void*)&s.b;
+ constexpr void *cv = (void*)&s.c;
constexpr bool v1 = null < (int*)0;
- constexpr bool v2 = null < pv; // expected-error {{constant expression}}
expected-note {{comparison between 'nullptr' and '&s.a' has unspecified value}}
- constexpr bool v3 = null == pv; // ok
- constexpr bool v4 = qv == pv; // ok
- constexpr bool v5 = qv >= pv; // expected-error {{constant expression}}
expected-note {{unequal pointers to void}}
- constexpr bool v6 = qv > null; // expected-error {{constant expression}}
expected-note {{comparison between '&s.b' and 'nullptr' has unspecified value}}
- constexpr bool v7 = qv <= (void*)&s.b; // ok
- constexpr bool v8 = qv > (void*)&s.a; // expected-error {{constant
expression}} expected-note {{unequal pointers to void}}
+ constexpr bool v2 = null < av; // expected-error {{constant expression}}
expected-note {{comparison between 'nullptr' and '&s.a' has unspecified value}}
+ constexpr bool v3 = null == av; // ok
+ constexpr bool v4 = bv == av; // ok
+ constexpr bool v5 = bv >= av; // cxx11-error {{constant expression}}
cxx11-note {{unequal pointers to void}}
+ constexpr bool v6 = bv > null; // expected-error {{constant expression}}
expected-note {{comparison between '&s.b' and 'nullptr' has unspecified value}}
+ constexpr bool v7 = bv <= (void*)&s.b; // ok
+ constexpr bool v8 = bv > (void*)&s.a; // cxx11-error {{constant expression}}
cxx11-note {{unequal pointers to void}}
+ constexpr bool v9 = cv > bv; // expected-error {{constant expression}}
expected-note {{comparison between '&c' and '&s.b' has unspecified value}}
+ constexpr bool v10 = cv <= (void*)&s; // expected-error {{constant
expression}} expected-note {{comparison between '&c' and '&s' has unspecified
value}}
}
// - an assignment or a compound assignment (5.17); or
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index 83b71e7c122d1e..12075b5aa0451e 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -14964,7 +14964,7 @@ <h2 id="cxxdr">C++ defect report implementation
status</h2>
<td><a
href="https://cplusplus.github.io/CWG/issues/2526.html";>2526</a></td>
<td>C++23</td>
<td>Relational comparison of <TT>void*</TT> pointers</td>
- <td class="unknown" align="center">Unknown</td>
+ <td class="unreleased" align="center">Superseded by <a
href="#2749">2749</a></td>
</tr>
<tr id="2527">
<td><a
href="https://cplusplus.github.io/CWG/issues/2527.html";>2527</a></td>
@@ -15984,7 +15984,7 @@ <h2 id="cxxdr">C++ defect report implementation
status</h2>
<td><a
href="https://cplusplus.github.io/CWG/issues/2696.html";>2696</a></td>
<td>dup</td>
<td>Relational comparisons of pointers to <TT>void</TT></td>
- <td class="unknown" align="center">Unknown</td>
+ <td class="unreleased" align="center">Duplicate of <a
href="#2749">2749</a></td>
</tr>
<tr id="2697">
<td><a
href="https://cplusplus.github.io/CWG/issues/2697.html";>2697</a></td>
@@ -16302,7 +16302,7 @@ <h2 id="cxxdr">C++ defect report implementation
status</h2>
<td><a
href="https://cplusplus.github.io/CWG/issues/2749.html";>2749</a></td>
<td>DR</td>
<td>Treatment of "pointer to void" for relational comparisons</td>
- <td class="unknown" align="center">Unknown</td>
+ <td class="unreleased" align="center">Clang 19</td>
</tr>
<tr id="2750">
<td><a
href="https://cplusplus.github.io/CWG/issues/2750.html";>2750</a></td>
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